Geology, isotope geochemistry and ore genesis of the Shanshulin carbonate-hosted Pb–Zn deposit, southwest China
Geology, isotope geochemistry and ore genesis of the Shanshulin carbonate-hosted Pb–Zn deposit, southwest China
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DOI：
10.1016/j.oregeorev.2014.05.012
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发表时间：
2014-12
影响因子：
3.3
通讯作者：
Jiaxi Zhou;Zhilong Huang;Zhi-Cheng Lv;Xiangkun Zhu;JianGuo Gao;H. Mirnejad
中科院分区：
文献类型：
--
作者：
Jiaxi Zhou;Zhilong Huang;Zhi-Cheng Lv;Xiangkun Zhu;JianGuo Gao;H. Mirnejad
杉树林铅锌存款矿床产于上石炭统黄龙组白云岩和白云岩中，位于扬子地块西部，贵阳以西约270 km。矿体沿着于渭水区域断裂带的高角度逆冲断层及观音山背斜西北部。硫化矿石主要由闪锌矿、黄铁矿、方铅矿等矿物组成，并伴有方解石和少量白云石。杉树林存款区已发现22个矿体，含硫化物矿石270万吨，品位0.54 - 8.94 wt.%。Pb和1.09至26.64重量% Zn.方解石的δ 13 CPDB和δ 18 OSMOW值分别为-3.1 ~+2.5 ‰和+18.8 ~+26.5 ‰。这些值高于地幔和沉积有机质，但与海相碳酸盐岩的δ 13 CPDBvs相似。δ 18 OSMOW图解表明，热液中的碳很可能来自碳酸盐围岩。闪锌矿和方铅矿的δ 34 SCDT值分别为+ 18.9 ~+ 20.3‰和+ 15.6 ~+ 17.1‰。这些值表明，碳酸盐岩是最有可能的硫源。闪锌矿-方铅矿共生矿物对的δ 34 SCDT值表明硫化物的沉积是在化学平衡条件下进行的。根据闪锌矿-方铅矿矿物对计算的硫同位素热力学平衡分馏温度范围为135 - 292 °C，与以前的流体包裹体研究一致。高于100 °C的温度排除了通过细菌硫酸盐还原（BSR）获得硫，并且表明热液流体中的还原硫最有可能通过热化学硫酸盐还原（TSR）提供。12个闪锌矿样品的δ 66 Zn值相对于JMC 3- 0749 L锌同位素标准为0.00 ~+ 0.55‰（平均+ 0.25‰）。Ⅰ ~ Ⅲ期闪锌矿δ 66 Zn值分别为0.00 ~+ 0.07‰、+ 0.12 ~+ 0.23‰和+ 0.29 ~+ 0.55‰，表明晚期闪锌矿的Zn同位素组成较早期闪锌矿重。锌同位素值的变化可能是由于动力学罗利分离结晶。硫化物样品的206 Pb/204 Pb、207 Pb/204 Pb和208 Pb/204 Pb比值分别为18.362 ~ 18.573、15.505 ~ 15.769和38.302 ~ 39.223。研究区存款铅同位素比值图覆盖了上地壳、造山带和地幔铅演化曲线，在207 Pb/204 Pb-206 Pb/204 Pb图上与元古宙褶皱基底岩、泥盆系-下二叠统沉积岩和中二叠统峨眉山溢流玄武岩重叠。这一观察结果表明，铅金属的来源是混合的。闪锌矿样品的87 Sr/86 Sr 200 Maratio范围为0.7107至0.7115，与经过年龄校正的泥盆纪至下二叠统沉积岩相似（0.7073 ~ 0.7111），高于经年龄校正的中二叠世玄武岩（0.7039 ~ 0.7078），低于经年龄校正的元古宙褶皱基底（0.7243 ~ 0.7288）。因此，Sr同位素数据支持混合来源。地质和同位素地球化学研究表明，杉树林存款是一个碳酸盐岩容矿、逆冲断层控制、层控、后生、流体和金属混合成因的高品位存款矿床。
The Shanshulin Pb–Zn deposit occurs in Upper Carboniferous Huanglong Formation dolomitic limestone and dolostone, and is located in the western Yangtze Block, about 270 km west of Guiyang city in southwest China. Ore bodies occur along high angle thrust faults affiliated to the Weishui regional fault zone and within the northwestern part of the Guanyinshan anticline. Sulfide ores are composed of sphalerite, pyrite, and galena that are accompanied by calcite and subordinate dolomite. Twenty-two ore bodies have been found in the Shanshulin deposit area, with a combined 2.7 million tonnes of sulfide ores grading 0.54 to 8.94 wt.% Pb and 1.09 to 26.64 wt.% Zn. Calcite samples have δ13CPDBand δ18OSMOWvalues ranging from − 3.1 to + 2.5‰ and + 18.8 to + 26.5‰, respectively. These values are higher than mantle and sedimentary organic matter, but are similar to marine carbonate rocks in a δ13CPDBvs. δ18OSMOWdiagram, suggesting that carbon in the hydrothermal fluid was most likely derived from the carbonate country rocks. The δ34SCDTvalues of sphalerite and galena samples range from + 18.9 to + 20.3‰ and + 15.6 to + 17.1‰, respectively. These values suggest that evaporites are the most probable source of sulfur. The δ34SCDTvalues of symbiotic sphalerite–galena mineral pairs indicate that deposition of sulfides took place under chemical equilibrium conditions. Calculated temperatures of S isotope thermodynamic equilibrium fractionation based on sphalerite–galena mineral pairs range from 135 to 292 °C, consistent with previous fluid inclusion studies. Temperatures above 100 °C preclude derivation of sulfur through bacterial sulfate reduction (BSR) and suggest that reduced sulfur in the hydrothermal fluid was most likely supplied through thermo-chemical sulfate reduction (TSR). Twelve sphalerite samples have δ66Zn values ranging from 0.00 to + 0.55‰ (mean + 0.25‰) relative to the JMC 3-0749L zinc isotope standard. Stages I to III sphalerite samples have δ66Zn values ranging from 0.00 to + 0.07‰, + 0.12 to + 0.23‰, and + 0.29 to + 0.55‰, respectively, showing the relatively heavier Zn isotopic compositions in later versus earlier sphalerite. The variations of Zn isotope values are likely due to kinetic Raleigh fractional crystallization. The206Pb/204Pb,207Pb/204Pb and208Pb/204Pb ratios of the sulfide samples fall in the range of 18.362 to 18.573, 15.505 to 15.769 and 38.302 to 39.223, respectively. The Pb isotopic ratios of the studied deposit plot in the field that covers the upper crust, orogenic belt and mantle Pb evolution curves and overlaps with the age-corrected Proterozoic folded basement rocks, Devonian to Lower Permian sedimentary rocks and Middle Permian Emeishan flood basalts in a207Pb/204Pb vs.206Pb/204Pb diagram. This observation points to the derivation of Pb metal from mixed sources. Sphalerite samples have87Sr/86Sr200 Maratios ranging from 0.7107 to 0.7115 similar to the age-corrected Devonian to Lower Permian sedimentary rocks (0.7073 to 0.7111), higher than the age-corrected Middle Permian basalts (0.7039 to 0.7078), and lower than the age-corrected Proterozoic folded basement (0.7243 to 0.7288). Therefore, the Sr isotope data support a mixed source. Studies on the geology and isotope geochemistry suggest that the Shanshulin deposit is a carbonate-hosted, thrust fault-controlled, strata-bound, epigenetic, high grade deposit formed by fluids and metals of mixed origin.